- J -
J-hook headgear A (primarily) extraoral appliance defined by a pair of metallic components, each in the shape of the letter 'j', that deliver force bilaterally to anterior, intraoral sites.
jackscrew Synonymous with expansion screw.
jaw A common term for either the maxilla (upper jaw) or mandible (lower jaw).
jaw relationship The position of the upper jaw in relationship to the lower jaw; usually an anters-posterior or transverse assessment.
joint symptoms A generalizing term referring to various aspects of TMJ dysfunction, internal derangement or other conditions involving the TMJ.
jumping the bite The correction of a crossbite brought about by horizontal movements of teeth and, occasionally, the jaw, to their correct position.
jumperA spring appliance attached to fixed appliances to move teeth similar to a Herbst appliance developed by J. J. Jasper.
- K -
key ridge The most inferior point on the zygomatic process of the maxilla as seen in a lateral cephalometric radiograph; the craniometric point zygomaxillare.
Kloehn headgear See Headgear. 
